1. Technical Field
This invention relates to continuous processes using wiped-surface reactors for free radical graft polymerization of polyolefins, and to graft copolymers thereby produced. In another aspect, this invention relates to polymerizable olefins containing fluoroaliphatic groups, and copolymers thereof.
2. Description of the Related Art
Processing or production of polymeric resins using wiped-surface reactors such as screw extruders and twin screw extruders is well known (such processing is often called reactive extrusion). Twin screw extruders and their use in continuous processes such as graft polymerization, alloying, bulk polymerization of vinyl monomers, and condensation and addition reactions are generally described in Plastics Compounding Jan./Feb. 1986, pp. 44-53 (Eise et al.) and Plastics Compounding, Sept./Oct. 1986, pp. 24-39 (Frund et al.). Graft reactions are said to be carried out by first melting a polymeric species in the initial stages of an extruder, injecting a peroxide catalyst into the extruder, and mixing in a monomer under high shear conditions. Advantages of the twin screw extrusion process are said to include narrow distribution of molecular weight, improved melt-flow properties, consistent process control, and continuous processing.
Graft polymerization reactions of polyolefins with various monomers using wiped-surface reactors are known. Such grafting is said to be useful in providing a polymer adduct with functionality to allow further modification of structure and properties. General mechanistic proposals regarding formation of these "mechanochemically synthesized" adducts are discussed in connection with grafting of maleic anhydride onto polypropylene in Polymer Prep., 1986, 27, 89 (Al-Malaika).
A number of particular free radical graft polymerization reactions have been reported. For example, U.S. Pat. No. 3,177,270 (Jones et al.) discloses a process for preparing graft copolymers by mixing an olefin polymer at a temperature between 110.degree. C. and 250.degree. C. while contacting the polymer with a minor proportion of a mixture comprising a monovinyl aromatic compound and optionally one or more other monomers such as acrylic acid, methacrylic acid, acrylonitrile, methyl methacrylate, methacrylonitrile, or maleic anhydride, the mixture having dissolved therein an organic peroxide.
British Pat. No. 1,292,693 (Steinkamp et al.) discloses use of a single-screw extruder to graft monomers such as maleic anhydride and acrylic acid onto polyolefins such as polypropylene in the presence of a suitable free radical initiator such as an organic peroxide. The product graft copolymers are said to have a melt flow rate (MFR) of at least 50% greater than the MFR of the base polymer.
U.S. Pat. No. 4,003,874 (Ide et al.) discloses modified polyolefins obtained by adding an unsaturated carboxylic acid or an anhydride thereof and an organic peroxide to a polyolefin and melting these components in an extruder. The polyolefin so obtained is said to adhere to glass fibers.
U.S. Pat. No. 4,146,529 (Yamamoto et al.) discloses a process for production of modified polyolefins by combining a polyolefin with one or more carboxylic acids or their anhydrides in an extruder in the presence of a radical producing agent and an organosilane.
U.S. Pat No. 4,228,255 (Fujimoto et al.) discloses a method for crosslinking a polyolefin, the polyolefin being a low density polyethylene or a polyolefin mixture containing a low density polyethylene, comprising reacting the polyolefin with an organic silane and an organic free radical initiator to form a silane-grafted polyolefin, then mixing the silane-grafted polyolefin with a silanol condensation catalyst. The mixture is extruded with heating in a single-screw extruder to provide a crosslinked polyethylene.